This study examined Theory of Mind in Williams syndrome (WS) and in normal chronological age-matched and mental age-matched control groups, using a picture sequencing task. This task assesses understanding of pretence, intention and false belief, while controlling for social-script knowledge and physical cause-and-effect reasoning. The task was selected because it is entirely non-verbal, so that the WS individuals could not rely on their good verbal skills when performing the task. Results indicated a specific deficit in understanding of false belief within the WS group. There was also evidence of heterogeneity in the WS group, with the false belief impairment restricted to only a particular subgroup of WS individuals identified originally by Porter, M., & Coltheart, M. (2005). Cognitive heterogeneity in Williams syndrome. Developmental Neuropsychology, 27(2), 275-306.